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ABSTRACT
Germination and plant growth responses in Ocimum spp. to seed pretreatments
The present investigation entitled “Germination and plant growth responses in Ocimum spp. to seed pretreatments” was conducted in the Department of Plantation Crops and Spices, College of Agriculture, Vellayani during 2018-2020 with the objective to standardize pretreatment of seeds for enhanced germination and plant growth in Ocimum tenuiflorum L. and Ocimum basilicum L.
The seeds of Ocimum tenuiflorum and Ocimum basilicum used for the study were sourced from Indian Institute of Horticultural Research, Bengaluru. The study was carried out in two phases: Phase 1- Pretreatment of seeds for enhanced germination, Phase 2- Evaluation of transplanted seedlings derived from pretreated seeds for enhanced plant growth. The seeds of both the species of Ocimum were subjected to various pretreatments viz., physical pretreatments, hormonal priming, biostimulant priming and biopriming (using microbes) prior to sowing. The seeds subjected to germination without any pretreatments were taken as the control.
In the first phase of the study, O. tenuiflorum seeds when exposed to physical treatments, pretreatment using concentrated sulphuric acid for 1 min recorded maximum germination (85.33 per cent). The hot water treatment (65oC for 10 min) recorded the highest seedling length (27.83 cm) and seedling vigour index (19.67) with a germination of 70.66 per cent. Among the hormonal treatments, seeds primed with GA3 @1500 μM recorded the highest germination (96 per cent), seedling length (29.63 cm) and seedling vigour index (28.42). In biostimulant seed priming, the untreated control recorded the highest germination (62.66 per cent) but the highest seedling length (31.29 cm) and seedling vigour index (11.46) were observed with salicylic acid (SA) @ 1500 μM . The . The . The . The seeds when subject to biopriming with microbes, seeds primed with Bacillus pumilus
recorded the best germination (72.66 per cent) and seedling vigour index (15.83). The highest seedling length (22.05 cm) was observed with Pseudomonas fluorescens, which was on par with that of B. amyloliquefaciens. Among all the pretreatments tried, GA3 @ 1500 μM was observed to give maximum germination (96 per cent) and seedling vigour index of 28.42, while SA @ 1500 μM recorded the highest seedling length (31.29 cm) in O. tenuiflorum.
When transplanted, O. tenuiflorum plants derived from hot water treated seeds recorded the highest number of branches (45.33), fresh (130.10 g) and dry (31.22 g) shoot biomass at harvest (90 DAS), among the physical treatments. Plants derived from GA3 @ 1500 μM treated seeds recorded the highest shoot biomass in terms of fresh (193.50 g) and dry (46.13 g) weight. The plants from SA @ 1500 μM μM primed seeds- gave the highest shoot biomass with fresh weight of 217.50 g and dry weight of 54.10 g, among various biostimulant priming treatments. Among the biopriming treatments, plants generated from the seeds treated with B. amyloliquifaciens, recorded the highest fresh (151.33 g) and dry (38.84 g) shoot biomass which was on par with that treated with P. fluorescens. Among all the pretreatments, plants derived from salicylic acid @ 1500 μM treated seeds recorded the highest shoot biomass.
When the O. basilicum seeds were exposed to physical treatments, water soaking treatment recorded the maximum seedling vigour index (16.13), while seedling length did not show any significant variation among the treatments. Among the hormonal priming, seeds exposed to BA @ 300 μM recorded the highest germination (80.67 per cent) and seedling vigour index (29.33). The maximum seedling length (39.03 cm) was observed in GA3@ 3000 μM . The seeds treated with SA @ 1500 μM recorded the highest germination (79.33 per cent) and seedling vigour index (27.92), among the biostimulant priming. Maximum seedling length (35.66 cm) was observed in SA @ 3000 μM and was and was and was and was on par with on par with on par with on par with SA @1500 μM . Among the biopriming treatments, seeds primed with B. velezensis recorded higher germination (82 per cent), seedling length (37.50 cm) and seedling vigour index (30.72), which were on par with P. fluorescens and
B. amyloliquifaciens. In O. basilicum, among all the pretreatments tried, biopriming with B. velezensis, B. amyloliquefaciens and P. fluorescens and SA @ 1500 μM recorded higher on par values with respect to germination per cent and seedling vigour index, while GA3 @3000 μM which recorded the highest seedling length.
When transplanted, plants of O.basilicum derived from the seeds exposed to physical treatments did not show any significant variation with respect to shoot biomass. In hormonal priming, the maximum fresh (146.00 g) and dry (17.39 g) shoot biomass were observed in plants generated from seeds primed with GA3 @ 3000 μM . On evaluation of plants derived from biostimulant priming, maximum fresh (134.17 g) and dry (15.95 g) shoot biomass were observed in SA@ 3000 μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM μM, which was on par with SA @ 1500 μM . Among the biopriming treatments, plants derived from seeds primed B. velezensis recorded the highest fresh (153.03 g) and dry weight (17.73 g) shoot biomass, which were on par with P. fluorescens and B. amyloliquefaciens. Among all the seed pretreatments tried, plants generated from the seeds primed individually with B. velezensis, B. amyloliquefaciens and P. fluorescens and SA @ 1500 μM recorded higher on par values with respect to shoot biomass.
In the study, among the various seed pretreatments in O. tenuiflorum, GA3 @ 1500 μM recorded enhanced germination and plant growth, in terms of germination per cent, seedling length, seedling vigour index, plant height, number branches and shoot biomass. In case of O. basilicum, biopriming using B. velezensis, B. amyloliquefaciens and P. fluorescens recorded enhanced germination and plant growth, in terms of higher germination per cent, seedling length, seedling vigour index, leaf, stem and shoot biomass.